The present invention relates to a heat treatment method and device.
Semiconductor device fabrication processes generally include steps in which various treatments, such as oxidation, diffusion, CVD, etc. are made on semiconductor wafers, objects to be treated. Various treatment devices have been already proposed from the viewpoint of higher throughputs of such treatment steps, cleanness, space savings, etc. (see, e.g., Japanese Patent Publication No. 27121/1992, Japanese Patent Laid-Open Publication No. 133422/1992, Japanese Patent Laid-Open Publication No. 148717/1992, etc.)
The treatment device described in, e.g., Japanese Patent Laid-Open Publication No. 148717/1992 has, as shown in FIG. 20, a vertical heat treatment furnace 2 in a box-shaped handling chamber 1, and a carriers feed in/out opening 8 in the front side of the handling chamber 1, through which carriers 7 each holding a plurality of semiconductor wafers W vertical enter and exit the handling chamber 1. In this case, the semiconductor wafers W held vertical in the carriers must be horizontally transferred onto a wafer boat 5 which is an objects-to-be-treated holder to be loaded into and unloaded out of the vertical heat treatment furnace 2. To this end, as shown in FIG. 21, near the carriers feed in/out opening 8 there are provided posture changing mechanisms each comprising a mount 10 for a carrier to be mounted on and which is swung on the rotational center to thereby change the postures of the carrier 7 thereon so that the semiconductors wafer W held on the carrier 7 have its vertical posture and horizontal posture.
The posture changing mechanisms 9 swing the mounts 10 by 90 degrees into empty spaces S1 defined below the mounts 10 to thereby change the posture of the carriers. The thus-posture changed carriers by the posture changing mechanisms 9 are conveyed by conveying mechanisms 51 into an upper accommodation portion in a number necessary for a treatment. The carriers in the accommodation portion are conveyed one by one to the side of the heat treatment furnace, and the semiconductor wafers W in the carriers taken out one by one by a transferring mechanism 52 onto the wafer boat.
In this conventional treatment device, the mounts are swung downward to change the posture of the carriers, and sufficient empty spaces for the mounts to be swung downward is needed. In addition, a sufficient space to keep the conveying mechanisms from interfering with the carriers projecting on the swing along a set swing trajectory when the mounts are swung is needed on the side of the conveying mechanisms. Thus the conventional treatment device has a limit to space saving and accordingly to down-sizing. Long distances of the swing and the conveyance of the carriers make treatment times longer, which is a limit to improvement of throughputs, i.e., efficiency of treatments.
In the handling chamber of the conventional treatment device there are provided a first air cleaning unit which injects clean air let in at the top of the handling chamber from the outside, a second air cleaning unit which draws the clean air injected by the first air cleaning unit and injects the clean air downward along the carrier opening, and a third air cleaning unit which draws the clean air which has been injected by the second air cleaning unit and reached below is drawn through a bottom duct and injects the clean air horizontally from one side wall of the heat treatment furnace to the other side wall thereof, and an exhaust duct which exhausts outside at a back side the clean air which has arrived at the other side wall. An atmosphere in the treatment furnace is thus cleaned to reduce dust, whereby adhesion of particles to the semiconductor wafers W can be suppressed with a result that yields of semiconductor devices which tend to be increasingly micronized can be improved.
But in the conventional treatment device, clean air is several times passed through the air cleaning units, which makes it impossible to sufficiently prevent contamination of semiconductor wafers W by dust. Furthermore, impurity gases of organic compounds, such as boron compounds, etc. generated by the dust removing filters of the air cleaning units tend to increase although in small amounts. Preventive measures to this are needed.
Furthermore, because clean air is uninterruptedly circulated sequentially throughout the handling chamber, it is difficult that an atmosphere in the handling chamber cannot be confined separately in the carriers handling space and in the wafers handling space (objects-to-be-treated handling space) in which the heat treatment furnace is housed, and the semiconductor wafers W are transferred between the carriers and the wafer boat.